brief sprint C2: introduce billboard.Brief notification model + view_post marks-read on GET — TDD

Brief is the slide-down-banner record that connects an event (a Line freshly appended to a Post) to a user who needs to see it. It's the C3 attachment point for note-unlock + share-invite + future event sources; the banner JS (C3) reads the Brief shape to render kind-specific affordances. C2 lays the schema + the FYI-read contract; C3 hooks the senders.

Schema (billboard.Brief):
- owner FK→lyric.User (related_name='briefs') — required; whose attention this is for
- post  FK→billboard.Post (related_name='briefs') — required; where FYI navigates
- line  FK→billboard.Line (related_name='briefs', null=True) — the appended Line that triggered the Brief; nullable for share-invite-style flows where the Line write races behind the Brief
- is_unread BooleanField default=True — flips on view_post GET
- kind CharField (note_unlock | user_post | share_invite, default=user_post) — drives banner-side affordances
- title CharField (blank=True) — banner display title
- created_at DateTimeField (default=timezone.now) — Meta.ordering='-created_at'

view_post (the post-detail GET) now bulk-updates is_unread=False on every Brief where owner == request.user AND post == our_post AND is_unread=True. POST (the compose-a-new-Line path) intentionally does NOT mark read — the user is authoring, not reviewing.

Tests: BriefModelTest (7) covers defaults, kind choices include all three values, line nullability, owner+post requiredness, title field, __str__ shape. ViewPostMarksReadTest (5) covers the GET flips owner's unread Brief to read; doesn't flip other users' Briefs on the same post; doesn't flip Briefs on unrelated posts; idempotent for already-read; POST request does NOT mark read.

Auto migration billboard/0002_brief creates the table. 801-test IT regression green (789 + 12 new).

Code architected by Disco DeDisco <discodedisco@outlook.com>
Git commit message Co-Authored-By:
Claude Sonnet 4.6 <noreply@anthropic.com>

src/apps/billboard/migrations/0002_brief.py

@@ -0,0 +1,34 @@
+# Generated by Django 6.0 on 2026-05-08 21:34
+
+import django.db.models.deletion
+import django.utils.timezone
+import uuid
+from django.conf import settings
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('billboard', '0001_initial'),
+        migrations.swappable_dependency(settings.AUTH_USER_MODEL),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='Brief',
+            fields=[
+                ('id', models.UUIDField(default=uuid.uuid4, editable=False, primary_key=True, serialize=False)),
+                ('is_unread', models.BooleanField(default=True)),
+                ('kind', models.CharField(choices=[('note_unlock', 'Note unlock'), ('user_post', 'User post'), ('share_invite', 'Share invite')], default='user_post', max_length=32)),
+                ('title', models.CharField(blank=True, max_length=255)),
+                ('created_at', models.DateTimeField(default=django.utils.timezone.now)),
+                ('line', models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.CASCADE, related_name='briefs', to='billboard.line')),
+                ('owner', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='briefs', to=settings.AUTH_USER_MODEL)),
+                ('post', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='briefs', to='billboard.post')),
+            ],
+            options={
+                'ordering': ['-created_at'],
+            },
+        ),
+    ]